Electrical transformer



Feb. 17; 1942. I D. ANDER ELECTRICAL TRANSFORMER Filed Feb. 10, 1940 INVENTOR. DA LE A N 125/2 awwgwfl ATTORNEY.

" which I have referred,

Patented Feb. 17, 1942 UNITED STATES PATENT OFFICE;

2,213,245 I 1 ELECTRICAL TRANSFORMER/ Dalehnder, Bronx, N I Application February 10,'1ill0, Serial No. $1 8,267

This invention relates to electrical transformers and more particularly to variable'transformers embodyinga coil, the winding of which is high resistance bridge will I arcing at the contact.

made up of successive turns and over which turns a contact arm is mounted totravel'ln such manner that a contact carried thereby may be caused to traverse the successiveturns of the winding for the purpose of varying the voltage of the current passing through the transformer; Transformers of this general type are common to the art. They are generally so constituted that portions of'successive turns of the winding are left bare; so that a current carrying contact can engage directly with the wire of these turns. Considerable difiiculty, however, has heretofore been experienced with such transformers, due to their inability to accurately select one turn at a time. In practically every case, the movable contact has been such that a plurality of turns are bridged at all times by the movable contact or at least bridged part of the time, with the result that the turns thus bridged are short circuited. Short circuiting in this manner produces its of the invention.

excessive heat on the contact member and materially shortens the life thereof. Furthermore arcing, which is common to prior transformers, is destructive not only of the contact, but of the turns of the winding. v v The present invention is directed primarily to the movable currentcarr'ying member of the transformer, i. e., to the current carrying arm and the contact devices whereby the current is selectively conducted from the individual turns of the winding. The'primary object of the invention is to provide apparatus which will select one turn at a time'without detrimental short cirwrung of adjacent turns at any time and capable of carrying current to one particular turn only. important advantage of such an arrangement is that adjacent coils are not'shorted.

' by the movable contact and there is consequently absent that resistance which, in all prior transformers. has produced the undesirable heat to Another object of the invention is to provide ,acontact member appropriate for cooperation with a transformer winding in such manner that such contact can electrically engage with only one turn at a time.

Another-object of the inventionis to provide a relatively high resistance bridge, so associated with the contact through which current is normally passed, that, during the period that the v contact is moving from one turn to the next, this Another object of the invention is to provide a plurality of contacts, all mounted on the same movable arm and soassociated with one another that they will collectively tap and carrycurrent from one turn of the winding at a time, without short circuiting successive turns at any time. The advantage of this arrangement is that the individual contacts may be made relatively small, but the several contacts will nevertheless collectiveiy have sufllcient surface or line engagement with any particular turn to eflectually carry the current load without undue heating.

Features of the invention, other than those adverted to, will be apparent from the hereinafter detailed description and claims, when read in conjunction with the accompanying drawing.

The accompanying drawing illustrates one practical embodiment of the invention, but the construction therein shown is to be understood as illustrative, only, and not as defining the lim- Figure 1 is a fragmentary perspective view showing the present invention incorporated in transformer construction. a

Figure 2 is a longitudinal central vertical section in the plane of the line'2--2 of. Figure l, with associated contacts in elevation and cooperating with a portion of a turn of the winding.

Figure 3 is a like section in the plane of the line 3-4 of Figure 3, showing details of the high resistance bridge. 1 I

Figure 4 is a perspective detail of. a carrier for Y the bridge roller.

Fi ures is a like viewot brushholder employed. 1

Figure 6 is a diagrammatic perspective showing the manner in which the contacts cooperate with adjacent turns of the coil.

The present invention may be associated with either acylindrical winding or a straight winding audit is not limited to the particular type of transformer with which it maybe employed. However, for the purpose of illustration,;l'. have shown the invention in Figure 1 as associated with a cylindrical winding, a number of .turns of which are indicated by the reference character i. These turns, which constitute a succession of current carrying members, are wound about a suitable core of annular form with appropriate end plates 2 and between the end plates 2 the 7 turns are uncovered for cooperation with a movable contact of the transformer. The turns are,

however, insulated with respect to one another in any suitable and conventional way. Trans- !ormers or this type commonly have a movable arm 8 comprising sections to and lb, the latter of which is carried by a coaxial pivot 4. An insulation strip I is interposed between these sections, whereby that portion of the arm, which carries the movable contacts, is insulated from the pivot. Current is fed to the movable contacts through a cable lead i. The structure, as thus far described, my be conventional and no claim is made thereto, apart from the present invention which will now be explained in detail.

According to the present invention, there is mounted rigi ly at the outer end or the arm I a contact holder 1. This contact holder is of hollow rectangular form and has an open bottom. In the holder is seated one or more contacts C and C. Two such contacts are shown, although more or less may be employed without departing from this invention. In any event, they are tact carries a binding post It and of the holder and are connected to woven current leads I! which form branches the main lead I. The contacts or leads II are insulated from the section 3a of the arm I,

laid secflon oi the arm is live."

on tacts are illustrated in perspective in PIgure 6. Each embodies a metal contact strip II, in lace abutting relation with one side of s ggy distant side or the insulating strip is a metal face plate It. In i'ace abutting relation to the back suri'ace o! the contact strip It is a metallic nller block II and the binding post II is in the form or a bolt, naming through the entire assembly with a oolmtersunkhead with a nut II serving to bind all e! the parts together, so that they become a rigid unit. The lower ends of the contact strip I and the insulating strip II are collectively chamfered or beveled to form a wedge shape, indieated at II, and adapted to extend below the lower edge or the filler block to cooperate with the successive turns I o! the winding, after the manner shown in Figure 8.

The contacts are positioned in th holder I in the reversed relation shown in Figure 8, with their wedge shaped end extending into the adiacent spaces between the consecutive turns I, la and lb or the winding and with the spacing between the apices of such wedges slightly less than the distance between centers oi the consecutive turns 0! the winding. This is the normal current-carrying position 0! the parts. With the contacts at rest, the contact plates ll of the contacts C and C will be in electrical engagement with the turn Ia, while the dielectric strips II of these two contacts insulate the plates II from contact with the turns I and lb, adjacent to but on opposite sides 0! the current carrying turn la. When the parts are in this position, short circuitbinding posts extend through slots II in ing between consecutive turns is impossible and current will be led to the intermediate turn in to the exclusion of all other turns.

When the parts are in current carrying relation to any particular turn, both the contacts C and C will carry part 01' the current from that turn and thus minimize resistance to current flow with consequent minimum heating.

When the arm 8 is moved as described, there are intervals, as the contacts pass to successive turns, when the current flow is interrupted. In the handling of high voltages, this may cause a tendency to undesirable arcing. I have thereiore shown in the drawing means whereby this may be minimized and practically eliminated. I accomplish this result by associating with the movable arm a roller 20 or carbon or some other resistance material capable of carrying current and bridging the consecutive turns, but with its resistance so high that, when the metallic parts of the contacts C and C' are in engagement with one turn oi the winding, all the current will flow through these contacts rather than through the high resistance roller 20.

The roller II is supported for rotation in a yoke 2| mounted for movement radially oi! the coil within the conilnes oi. a housing 22. This housing holds the yoke against lateral movement and is in turn rigid with the arm 3. Studs 23 on the yoke extend loosely through holes in the housing and arm and guide it for such radial movement while springs N hold the roller in contact with he coil. The roller is supported within the yoke on a spindle II, the outboard end or which carries a conducting roller 20 and with this roller cooperates a brush 2! carried by a brush holder 2| supported on the yoke 2 I, all as clearly shown in Figures 3, 4 and 5. The brush has a pigtaii connection with the arm 3 to ground the same thereon.

As the movable arm I is rotated about the pivot 4, the high resistance roller It will traverse the turns of the winding in succession, at all times bridging two adjacent turns of the winding on the low voltage side of the turn which the contacts are leaving. In this manner arcing is practically eliminated.

Experience has shown that by the use of a plurality 01' contacts constructed as described, and the concurrent employment of the high resistance roller bridge, the structure will have an unbelievably long life. This is due to the fact that there is very little heating of the contacts C and C and, because 0! the absence of arcing, there is relatively little pitting or burning away thereof. The spring actuated contacts move over the several turns in succession after the manner 01 a ratchet and the pressure of the springs behind these contacts serve to hold the movable arm in any current carrying position in which it may be placed.

I have shown in the drawing the preferred form of this invention embodying two contacts C and C, reversed with respect to one another, so as to electrically cooperate with the opposite sides of one turn at a time. I! desired, however, I may position these contacts in the holder in the same relation, 1. e., not reversed. When this is done, the same sides of both contacts will cooperate with the same side of one winding at a time and a satisfactory result will be obtained. I prefer, however, to use th structure as shown in the drawing, as it appears to better distribute the wear and to produce a better balance in the opration oi the structure.

In the drawing the contacts of this invention are shown as cooperating directly with the turns of a transformer winding. I may, however, if desired take taps on of successiv turns of a transformer and lead them to current carrying members arranged in spaced relation and then have the contacts and cooperating resistance roller cooperate with these current carrying members instead of directly with the turns of the transformer. In other words, the present I invention is useful either directly with the winding of a transformer or with current carrying members connected thereto.

The foregoing detailed description sets forth the invention in its preferred practical form, but I the invention is to be understood as fully commensurate with the appended claims.

Having thus fully described the invention, what I claim as new and desire to secure by Letters Patent is:

1. An electrical transformer comprising an annular winding of substantially circular wire having turns with a portion of each turn uncovered for cooperation with movable contacts, a movable arm pivoted coaxially of the annular winding to travel circumferentially thereof. a pair of spring pressed contacts carried by the arm and impelled into engagement with the uncovered portion of said winding, each of said contacts comprising conductive and dielectric strips positioned back to back and rigidly secured to one another with their winding-engaging ends collectively wedge shaped to fit between successive turns of the winding with the conductive strip in electrical engagement with one turn and the associated dielectric strip in dielectric engagement with the next adjacent turn of the winding, the several contacts being so positioned on said arm that the apices of their wedge shaped ends are spaced apart in a direction circumferentially of the wind- 4 ing a distance less than the distance between centers of the consecutive turns of the winding, and with the conductive strips of the several contacts arranged in directions facing a common interposed turn of the winding to simultaneously 1 engage with the opposite sides thereof.

2. An electrical transformer comprising an annular winding of substantially circular wire having turns with a portion of each turn uncovered for cooperation with movable contacts, a movable 5 arm pivoted coaxially of the annular winding to travel circumierentially thereof, a pair 01' spring pressed contacts carried by the arm and impelled into engagement with the uncovered portion of said winding, each of said contacts comprising conductive and dielectric strips positioned back to back and rigidly secured to one another with their winding engaging ends collectively wedge shaped to fit between successive turns of the winding with the conductive strip in electrical engagement with one turn and the associated dielectric strip in dielectric engagement with the next adjacent turn of the winding, and a roller carried by said arm in electrical connection with said contacts and spring pressed into engagement with the uncovered portion of the winding, said roller having a relatively high resistance as compared to the current carrying strips of said contacts and positioned to engage with the same turn of the winding as is engaged by the conductive strips of the contacts and also one adjacent turn.

3. An electrical transformer comprising an annular winding of substantially circular wire having turns with a portion of each turn uncovered for cooperation with movable contacts, a movable arm pivoted coaxially or the annular winding to travel circumferentially thereof, a pair of spring pressed contacts ,carried by the arm and impelled into engagement with the uncovered portion of said winding, each of said contacts comprising conductive and dielectric strips positioned back to back and rigidly secured to one another with their winding engaging ends c01- lectively wedge shaped to fit between successive turns of the winding with the conductive strip in electrical engagement with one turn and the associated dielectric strip in dielectric engagement with the next adjacent turn of the winding, the several contacts being so positioned on said arm that the apices of their wedge shaped ends are spaced apart in a direction circumferentially of the winding a distance less than the distance between centers of the consecutive turns of the winding, and with the conductive strips of the several contacts arranged in directions facing a common interposed turn of the winding to simultaneously engage with the opposite sides thereof, and a roller carried by said arm in electrical connection with said contacts and spring pressed into engagement with the uncovered portion of the winding, said roller having a relatively high resistance as compared to the current carrying strips of said contacts and positioned to engage with the same turn of the winding as is engaged by the conductive strips of the contacts and also one adjacent turn.

DALE ANDER. 

